This invention relates in general to a fuel injector assembly, and more specifically to a fuel injector assembly having at least one spring seat allowing spring rotation and alignment.
It is known to use a coil spring between an armature and an adjusting tube in a conventional fuel injector assembly. The spring is disposed between an end of the adjusting tube and a void in the armature. By this arrangement, the adjusting tube applies a reaction force on an upstream end of the spring, and the downstream end of the spring applies a biasing force on the armature.
One disadvantage of springs in conventional fuel injector assemblies is the increased frictional forces that are caused by the active coils of the spring rubbing against cavity walls (e.g., spring guides positioned inside of the coils or surrounding the coils) and by over-constraining the ends of the spring. Constraining the ends of coil springs to remain parallel during spring compression creates undesirable parasitic forces such as off-axis reaction forces and torques. As it is used in connection with the present invention, the expression xe2x80x9coff-axisxe2x80x9d refers to a direction that is not coincident with a centerline of the armature, i.e., the axis along which the armature moves.
The natural twisting of conventional fuel injector springs, which is caused by spring compression, can adversely affect injector performance by forcing the armature needle to rotate a prescribed amount during opening, and then rotate oppositely during closing. Thus, another disadvantage of conventional fuel injector spring arrangements is that the needle is prevented from freely rotating, thereby degrading sealing performance and increasing wear between the needle and its seat. Moreover, the off-axis reaction forces urge the armature away from optimum alignment, thus further degrading sealing performance, causing wear of the upper and lower armature guiding surfaces, and increasing wear between the needle and the seat.
For these reasons, it is desirable to counteract the effect of parasitic forces by allowing movement of a fuel injector assembly spring so as to substantially eliminate the effect of off-axis forces, and without increasing the frictional forces on the spring.
An object of the present invention is to eliminate or minimize the effect of parasitic forces resulting from the compression and extension of a coil spring in a fuel injector. Another object is for a fuel injector spring to generate a biasing force that is substantially coaxial with the movement of a fuel injector armature.
The present invention provides a fuel injector having a fuel inlet, a fuel outlet, and a fuel passageway extending along an axis between the fuel inlet and the fuel outlet. The fuel injector comprises a body having an inlet portion, an outlet portion, and a neck portion disposed between the inlet portion and the outlet portion; an armature disposed within the neck portion of the body and displaceable along the axis relative to the body; a spring disposed within the neck portion and applying a biasing force to the armature, the spring having a downstream end disposed proximate the armature and an upstream end opposite from the downstream end; an adjusting tube disposed within the neck portion of the body and proximate to the upstream end of the spring, the adjusting tube varying the biasing force applied by the spring to the armature; and a first spring seat engaging a first one of the downstream and upstream ends, the spring seat permitting spring movement counteracting parasitic forces arising due to spring compression and extension.
The present invention also provides a method of forming a fuel injector having a fuel inlet, a fuel outlet, a fuel passageway extending along an axis between the fuel inlet and the fuel outlet. The fuel injector including a body having an inlet portion, an outlet portion, a neck portion extending between the inlet portion and the outlet portion, an adjusting tube, and an armature. The method comprises disposing an armature displaceable along the axis relative to the body within the neck portion; disposing a spring applying a biasing force to the armature within the neck portion, the spring having a downstream end disposed proximate the armature and an upstream end opposite from the downstream end; and providing a first spring seat engaging a first one of the downstream and upstream ends of the spring, the first spring seat permitting spring movement such that the biasing force is applied substantially along the axis.